Power transmission



May l19v1943. R. c. GRIFFITH POWER TRANsMssIoN Filed Ma'rch 16, 1938 INVENTOR RAYMOND C. GRIFFITH` ATTORNEY Patented May 11, 1943 POWER TRANSMISSION Raymond c. Griffith, Detroit, Mich., assignor to j Vickers Incorporated, Detroit, Mich., a corporation of Michigan Application March 16, 1938, Serial No. 196,121- y ('Cl. GII-52) Z Claims.'

This invention relates to power transmissions and more particularly to those of .the fluid type wherein a power transmitting fluid, such as oil, and hereinafter referred to as such, is utilized forthe transmission of power between one or more pumps and one or nore motors.

This invention is particularly concerned with a hydraulic transmission system for operating a in it is desired to move the working member forwardly on a work stroke, in response to manual initiation, to automatically reverse the work member at the completion of the forward stroke, and to automatically stop the work member at the end of the return stroke. l

It has been custom-ary heretofore in hydraulic transmissions for operating presses to utilize a spring-biased, four-way valve for starting, stopping, and reversing the flow ofuid to the press operating motors and to provide the Valve with a spring bias in one direction, and with a latch for holding the valve in one extreme position against lthe bias. The valve may then be manu- 4ally operated to latched position which causes a flow of fluid to the main ram for performing the forward .pressing stroke. At the completion of the forward stroke either the movement of the press platen or the pressure developed as the platen bottoms is utilized to release the. latch permitting the valve to shift to its opposite position under its spring bias,y thereby reversing the flow ofiluid and returning the platen toopen position. As the end of the return stroke is ,l reached the movement of the platen is utilized to operate the valve to center or press-stopping position.

Considerable diculty has been experienced with press operating systems of this character since the valve depends for its operation at the end of the cycle upon movement of the press. On the other hand, as soon as the valve approaches the position where uid flow is cui; oil", no moremovementof ythe press can take place to insure complete closing of Ithe valve. Attempts to avoid I this difliculty have heretofore' made use of complicated snap actingmechanism or have endeavored to balance one 'spring against another with l. ensuing Atrouble due to wear, lvarying friction in the valve, varying visc-osity of spring characteristics etc. s

It is an object of the present invention to p rovide a vpower transmission system', particularly adapted for operating a press in'which the above dilculties are avoided.

A further object -is to provide an improved the oil, y varying press-or other reciprocating work machine where- X valve ofl simple and reliable construction providing a novel detent mechanism and incorporating, as well, an improved and simplified dashpot construction for cushioning the movement of the valve member when the latch is tripped.

Further objects and advantages of the present invention will be apparent from the following description, reference being hadto the, accompanying drawing wherein a preferred form of the present invention is clearly shown.

In the drawing:

Figure 1 is a diagrammatic view of a power transmission system incorporating a preferred form of the presen-t invention. v

Figure 2 is an enlarged sectional view showing the latch mechanism of a valve incorporated in Figure 1. I l

Figure'3 is an enlarged view of the dashpot mechanism of the valve, showing the parts in a different position.

A pump I adapted to vbe driven by a suitable prime mover, not shown, withdraws oil through a suction conduit I2 fromga tank I4 and delivers i ,the same through a pressure conduit I6. The

latter has 'a relief valve I8 incorporated therein for luy-passing oil to the' tank through a by-pass conduit '20 whenever a .predetermined pressure is exceeded in the line I6. 'I'he conduit I6 leads to the pressure port 22 of a four-way valve 24. Adjacent the pressure port 22 are a pair of cylinder ports 26 and 284 while beyond these ports are tank ports 30 and 32. The ytank ports 30 and 32 communicate with the tank by a conduit 3l.

Port 26 leads by a conduit 36 to the head end of a main press cylinder 38,- having a main ram 40 reciproc-ably mounted therein. Conduit 36 also hasv branches 42 and 44 extending to the head ends of a pair of push back cylinders 46 and 48, having pushback pistons 50 and 52. The ram 40 and pistons 50 'and 52 are connected .to the press platen indicated at 54 inthe well known mannen 48 connect by conduits 56'and 58 with the pont 2S of the valve 24. The platen 54 carries a trip arm 55 for operating the control valves, later to be described.

Stationarily mounted on the frame ofthe press is a rotary, four-way, pilot valve 60, having a pressure port P which connects Iby a conduit 62 with conduit 56. connects by a conduit 64 -wi-th'the tank I4. Cylinder port I of the valve-'60 connects by a con-duit 66 with the rod end. of a stationary cylinder 68 mounted in line-with the valve 24. Cylinder .port 2 of the valve 6I! connects by a The rod ends of the cylinders 46 and" The tank port T of the valve.

adapted to be shifted by the arm 55 as the latten approaches and leaves'the top of the .press stroke. The valve 24 has a cylinder bore 16 into which the ports 22, 26, 26, 66 and 62 open and in which is slidably mounted a spool 16 having piston heads 86 and 62 thereon, adapted to control communication between the ports in the well known manner. In its central position, illustrated, the spool 62 blocks the port 26 while the spool 66 being narrower in width than the port 26, permits communication between the ports 22, 26 and.66. With the spool moved downwardly port 2611s opened to port 22'while port 26 is opened to port 66 only. -With the spool moved upwardly the reverse connections are established. The spool 16 carries the stem 14 by a loose pin connection iat 64 which permits a slight degree o f radial play between the spool and the stem. Surrounding the stem 14 is a compression spring 66 which abuts at its lower end a collar 66 pinned to the stem 16. 'Ihe upper end of the spring 66A abuts a transverse washer-like member 96, mounted between the body 24 and the end-cap 92, which is secured to the body by suitable bolts, not shown. The member 66 is provided with a through-hole 94 through which the stem 14 extends with a considerable degree of clearance and is also provided with one or` more small transverse holes 95 extending from one side to the other thereof. About the hole 94 there is provided an enlarged bore 96 adapted to receive the piston-like end |66 o'f the spool 16.

At its upper end the spool l6 is provided with an integral stem portion |62 which is reduced as at |64 to form a shoulder |66, see Fig. 2. An

end-cap |66 is moxmted on the body 24 on its.

upper end and has a bore ||6 within which is slidably mounted a hollow sleeve-like member ||2, which, at its lower end surrounds the end portion |l4 of the stern |62. The sleeve ||2 is provided with diametric slots l|6 in which a pin ||6, secured to the stem ||4 may freely slide. A compression spring ||5 is interposed between the stemV ||4 and thesleeve ||2. At its lower Y end the sleeve ||2 is provided at a conical cam surface |26. Freely slidable in a bore |22 in the cap |66 is a cylindrical detentf|24 having 'a keyway |26, which may slide n a stationary pin |26. A spring |66 normally urges the detent to therleit in Fig. 2. The detent |24 is provided withan upwardly facing cam surface |62 cooperating with the conical cam surface |26. A shoulder |64 is adapted to engage the shoulder |66 when the latter moves upwardly a sulcient distance to permitthe detent |24 to move to the left. A stop washer |66 having a cut-out portion |66 to clear the detent |24 is positioned in the bottom of the bore ||6 and Vforms a guide for the stemportion ||4. s'

In operation, starting with the parts inthe position shown in'Figure 1 andi and with the Ypump |6 operating-oil is delivered from the conduitA I6 through thezport 22 and returns to the tank. by-passing around the piston 66 at the port- 26 and flowing through the port 66 and conduit 64-to thestank. pump is thus by-passed at' substantially, while the oil in the rod ends of the cylinders 46'and 46 is under a pressure created by the weight of the platen 64 due to theblocking of port 26.

When it is desired to start the press downwardly the lever 15 is operated to 4raise the stem 14 against the spring 66,'causing the detent |24 to engage its shoulder |34 beneath the shoulder |66. Oil is thereby directed from pressure line I6 through ports 22 and 26 and conduits 66, 42 and 44 to the head ends of the cylinders 66, 46 and 46. The platen 64, accordingly. descends, forcing oil out of-l the rod ends of cylinders 46 and 46 through conduits 56 and 66, ports 26 and 62 and conduit 34 to the tank. As the platen reaches the bottom of its stroke the arm 66 contacts the sleeve I2, as shown by dotted line, pushing the latter downwardly against the spring ||6 until the cam surface |26 by its co-action with the cam surface |62 retracts the detent |24. When this occurs the spring 66 is permitted to expand and the spool 16 moves downwardly to its extreme bottom position. As the spool approaches bottom position, the piston portion |66 enters the bore 66, trapping oil therein which is permitted to escape through the clearance between stem 14 a.nd` the hole 94, returning to the port 62 through the holes 96. This path may be givenany suitable resistance so that the last movement of the valve is hydraulically cushioned against shock.

In its lowermost position the valve 24 connects the pressure conduit |6 through ports 22 and 26 and conduits 56 and 66 to the rod ends of the `shown on the drawing.

pressure oil from the conduit A portion of the 66 passes through branch conduit 62, ports P and 2 and conduit 16 to the head end of cylinderl 66. The piston 12, accordingly, moves upwardly, shifting the valve stem. 14 and the valve spool 16 to the middle position illustrated. The weight of the platen and associated parts maintain suillcient pressure in the line 56 after valve 24 has centered to hold the piston 12 in its upper posi. tion.

It will be seen that tively moved to middle position and that considerable overlap of the piston 62, with the bore 16 at the upper edge of port 26, may berallowed, thus providing for ample sealing ofthe oil beneath the'piston 66 and 62. The point at which the piston 62 just closes the port 26 may be made to occur a little earlier Vthan the point at which the spool 66 just begins to open. port 22 to port 26 if desired, thus insuring that pump pressure will be available to operate the l y 66 and 62 right up' tothe point at which they become blocked. Obviously, while the pilot circuit is shown as receiving oil from the msn-back cylinder line 66, the same could be connected to any other supply of oil such as the line I6 or an While the form of embodiment ofthe invention as herein disclosed, 'constitutes va. preferred "-form, it is to be understood that other forms might be adopted, all coming within. the scope of the claims which follow.

the valve spool 16 is posi` push-back pistons a selected path, said element having lands spaced apart in a direction along said path, said casing What is claimed is as follows: 1. In a uid power transmission system the combination of asource of pressure fluid having high and low pressure sides, hydraulic motor means operable by iiuid from said source on either a forward stroke or a return stroke and-*subject to a continuous biasing force in a forward direction, directional controlmeans for directing the `flow of fluid from saidl source to the motor for operating said motor on aforward or on a return stroke, or for stopping the motor, said directionalA y from the motor is cut off and the pump is un'- loaded and in the third of which the uid is diiectedv to the motor forl a-return stroke, means biasing the control means to the tln'rdpositiom means for shifting the control means to the first position, a fluid motor for moving the control means to the middle position, and a pilot valve controlled bythe hydraulic motor aty the end of a return stroke to direct uid to operate said uid motor for moving said controlmeans to its middle position, said uid motor being operated by fluid placed under pressure in the return side of the hydraulic motor` by 'the biasing force acting on said hydraulic motor.

2. An improved operating system for a hydraulic motor of the type having aworking member, hydraulicmeans for advancing said member, hydraulic means for retracting said member, and a source of operating uid under pressure, which comprises the combination therewithof a main valve having a chamber, and a valve element movable back and forth in said chamber along having ports connected in groups bythe spaces between said landsv and covered and uncovered by the lands as they pass, one of said ports. being connected to said advancing means, another to said retracting means, another disposed between these two and connected to said, source, others beyond both of said first two ports and connected to exhaust, means operable on said element and urging it yieldingly into one end posiZtion in which it' connects said retracting means to said source and said advancing means to exhaust, and hold-.

ing it yieldingly in that position, a hydraulic device having a piston normally inoperative to oppose movement of said element into said one end position, but movable underlhydraulic pressure into a position in which it releasably limits movement of said element under the action of said urgnggmeans to an intermediate position in which a land closes said port connectedto said retracting means andsaid source port and said port connected to said advancing means are connected to exhaust, means including a valve controlled by said member and operable to connect said retracting means to said hydraulic-device and cause said movement of said piston when said member is retracted within a selected extent and to disconnect said retracting means Vfrom said hydraulic device when said-member is away from said selected extent ofv retraction, and means for moving .said element into the opposite end position in which it connects said source to saidV advancing means and said retracting means to. exhaust and holds said element releasably in that end position.

RAYMOND c, GRIP-HTH. V 

